JPH0411185Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention relates to a multi-channel ionization chamber type radiation detector, and in particular, even if there is a change in the ambient temperature of the detector, the adjacent parts of each electrode block The present invention relates to an ionization box type radiation detector suitable for keeping the pitch between the electrode plates unchanged and maintaining the same pitch as the pitch in the middle of the electrode block.

[Prior Art] Conventionally, an ionization chamber type radiation detector uses
It is widely used in so-called rotation-rotation type CT scanners, in which a beam tube and a detector are rotated around a subject while maintaining their relative positional relationship. The detectors in such CT scanners are arranged in an array in such a way that slight variations in the characteristics of each detector element can cause large fluctuations in the detector output, causing artifacts in the final CT image. Stability against external or external temperatures is required.

The detector itself is generally constructed as follows. That is, on each side of an electrode holding plate made of a pair of flat insulating materials, a large number of grooves are cut radially toward the radiation source at a pitch of, for example, several hundred microns. The signal electrode plates and the high voltage electrode plates are arranged in pairs in pairs, and signal electrode plates and high voltage electrode plates are alternately inserted between the opposing grooves and fixed with adhesive to form an electrode block. The number of elements in an electrode block is usually kept to around 100 elements due to available material dimensions, processing precision, and inspection and treatment when a defective element occurs.
Furthermore, in order to increase the number of elements to make a detector with several hundred or more elements, a plurality of electrode blocks are arranged in series to form an electrode assembly. The electrode assembly is housed in a closed space within the container and fixed to the container to form a detector. In this case, the container is filled and sealed with ionized gas at a pressure of several atmospheres or more. For this reason, the container has a main body with a box-shaped cylindrical cross section with one side open for convenient filling of ionized gas;
and a lid that closes the open surface. The lid is fixed to the open periphery of the container body with bolts with a sealing member interposed between the lid and the open surface of the container body, but when the electrode blocks are fixed, the electrode blocks are fixed from the outer surface of the lid, Because of the need to maintain the ionized gas sealing effect, all of the numerous bolts for fixing must also be sealed. However, since the lid needs to be removed for inspection of the electrode block, etc., it becomes difficult to maintain a predetermined sealing condition at the bolt portion each time the bolt is removed. For this reason, the following considerations have been made regarding the structure of the lid. That is, a flat lower plate, which is integrally fixed to the lid with bolts, is provided along the entire length of the inner surface of the lid to which the electrode block is attached, and the electrode block is attached to this lower plate. In this case, the fixing order is to first attach the lower plate and the electrode block with bolts, then attach the lower plate with the electrode block attached to the screw hole provided on the inner surface of the lid (closed space side) with bolts. Fix it. At this time, the screw holes provided in the lid do not penetrate through the lid. Next, the electrode block, lower plate and lid, which are fixed to each other, are housed in the main body of the container, and the lid and main body are fixed with bolts as described above.

The material of each part constituting the detector is generally ceramic for the electrode holding plate and aluminum for the reasons that the container absorbs little radiation and requires strength as a pressure container. Furthermore, since the lower plate mentioned above is integrally fixed to the lid of the container and is constructed as a part of the lid, it is preferably made of a material with the same coefficient of thermal expansion, and generally the same aluminum as the container is used. There is.

[Problems to be solved by the invention] The problems with such an ionization chamber type radiation detector are as follows.
When the ambient temperature changes, the pitch between adjacent electrode plates of each electrode block changes, creating a difference in pitch between the electrode blocks, which can cause artifacts in the final CT image. be. That is, the change in pitch is caused by the fact that the thermal expansion coefficients are significantly different due to the aforementioned difference in materials between the electrode block and the container. And, this pitch change is caused even if the contact surface between each electrode block and the lower plate is smoothed,
In addition, even if the tightening force of the bolts fixing the two is adjusted uniformly and the two are fixed so that they can slide and move within the range of play in the bolt holes, the distance between each electrode block and the lower plate is due to the difference in thermal expansion. This is an unavoidable phenomenon because the relative movement is caused by the difference in the amount of expansion and contraction of the electrode blocks, and the manner of the relative movement differs depending on each electrode block.This phenomenon occurs when the pitches between the electrode plates in adjacent parts of each electrode block are squeezed. This results in a difference in pitch in the middle of the electrode block, resulting in different characteristics between the detection elements in the electrode block.

The above-mentioned rotation-rotation method
In CT scanners, the detection characteristics of individual detection elements,
For example, in order to eliminate the effects of nonlinearity variations, measurements are taken in advance using a water phantom before measuring the subject, and this data is used to calibrate the data obtained by sampling. When the pitch changes, the characteristics of the detecting element change, which has the problem that it cannot be corrected by the above-mentioned calibration.

In view of the above-mentioned problems of the prior art, the present invention has been developed to prevent the pitch between adjacent electrode plates of each electrode block from changing even if the ambient temperature of the detector changes. An object of the present invention is to provide an ionization chamber type radiation detector that can maintain the same pitch as the pitch.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a pair of flat plate-shaped plates in which a large number of grooves are cut radially toward the radiation source on one side, and the grooves are arranged opposite to each other. an electrode block having an electrode holding plate, in which signal electrode plates and high voltage electrode plates are alternately adhesively fixed and held between opposing grooves of the electrode holding plate; and a box-shaped cylinder with one side open. a container made of a material having a larger coefficient of thermal expansion than the electrode holding plate; an electrode assembly including a plurality of the electrode blocks is placed in the container, In the ionization chamber type radiation detector, the radiation detector is fixedly fixed with bolts to the entire inner surface length of the lid through a flat lower plate made of the same material as the lid and integrally fixed to the lid, and is filled with ionized gas. A single bottom plate made of a material with a coefficient of thermal expansion that is the same as or similar to that of the electrode holding plate is interposed between the bottom plate and the electrode assembly, and between the bottom plate and the electrode assembly and the container and the bottom plate. The electrode blocks and the bottom plate are bolted to the bottom plate through the bottom plate so that each electrode block and the bottom plate can slide integrally between the bottom plate and the bottom plate. The contract is designed to be concluded at

[Operation] With the above configuration, the relative movement (slip) caused by the difference in thermal expansion coefficient between the electrode block and the container that occurs when the ambient temperature of the detector changes is as follows.

() Since the difference in thermal expansion coefficient between the electrode holding plate and the bottom plate of the electrode block is extremely small, they expand and contract by approximately the same amount, and there is practically no relative movement between them. In this case, the surface of the electrode holding plate among the contact surfaces between the two is made of ceramic and is therefore rough, making relative movement between the two difficult.

() Bottom plate and lid (directly, the lower plate is fixed integrally with the lid as described in the prior art)
Since there is a large difference in the coefficient of thermal expansion and the amount of expansion and contraction between the two is different, a relative movement occurs between the two. In this case, both the bottom plate and the bottom plate, which are integrally fastened to each electrode block with bolts, do not prevent relative sliding movement at the contact surface between the two, and therefore each electrode block and bottom plate are Moves integrally with the lower plate. Furthermore, the contact surfaces between the bottom plate and the lower plate can be processed to be smooth due to their materials, making relative movement between the two easier.

() When the ambient temperature of the detector changes, the difference in thermal expansion coefficient between the electrode block and the container causes the change in the pitch between the electrode plates, which conventionally occurs due to the adjacent parts of each electrode block being wrinkled. The effects of () and () above prevent this from occurring, and it becomes possible to maintain the pitch at the same pitch as the middle part of the electrode block.

[Example] Hereinafter, an example of the present invention will be described with reference to the accompanying drawings. In the figure, 1, 1 is a pair of flat electrode holding plates on which many grooves are cut radially toward the radiation source on one side with a pitch Pi of several hundred microns, and the grooves are arranged facing each other. , 2 is the electrode holding plate 1,
Signal electrode plates 1 and 3 are adhesively fixed between opposing grooves, electrode holding plates 1 and 1 are alternately connected to signal electrode plates 2 and 3.
A high voltage electrode plate is adhesively fixed between the opposing grooves of the . The electrode holding plates 1, 1, the signal electrode plate 2 and the high voltage electrode plate 3 form electrode blocks 4a, 4b.
(hereinafter referred to as electrode block 4a etc.). The pitch Pb between the signal electrode plate 2 and the high voltage electrode plate 3 between the adjacent electrode blocks 4a and 4b is set to be the same size as the pitch Pi at the intermediate portion of the electrode blocks 4a, etc. Reference numeral 5 denotes a box-shaped cylindrical main body with one side open, and 6 a lid that covers the open surface of the main body 5. As described in the prior art, the main body 5
It is fixed to the periphery of the open surface with bolts with a sealing member (not shown) interposed between the open surface and the open surface. Together with the main body 5, a container 7 having a sealed space inside is formed, and an electrode assembly 10 including an electrode block 4a and the like is housed in the sealed space.
The container 7 is made of a material having a larger coefficient of thermal expansion than the electrode holding plates 1, 1, and is filled with an ionized gas such as xenon gas at a pressure of several atmospheres or more. 8 is a flat lower plate made of aluminum alloy that is integrally fixed to the entire length of the inner surface of the lid 6 with bolts, as described in the above-mentioned prior art. Reference numeral 9 denotes a single (one-piece) bottom plate interposed between the lower plate 8 and the electrode block 4a, etc., and is made of a material with a thermal expansion coefficient that is the same as or similar to that of the electrode holding plates 1 and 1. There is. For example, electrode holding plate 1,
When 1 is ceramic with an alumina content of 99% and a thermal expansion coefficient of (6 to 9) × 10 ^-6 , the bottom plate 9 is a 45% Ni-Fe alloy with a thermal expansion coefficient of 6.8 × 10 ^-6 . or 9.4×10 ^-6 50% Ni-Fe alloy.

By interposing the bottom plate 9 between the electrode block 4a etc. and the lower plate 8, the lid 6 of the electrode block 4a etc.
To fix the electrode block 4a to the lower plate 8 via the bottom plate 9 with bolts, or after fixing the electrode block 4a etc. and the bottom plate 9 integrally with bolts, lower the bottom plate 9. It may be fixed to the plate 8 with bolts. In either case, if there is a difference in the amount of expansion or contraction between the bottom plate 9 and electrode assembly 10 and the container 7 and bottom plate 8 due to a difference in thermal expansion, the bottom plate 9 and electrode assembly 10 will Since there is no difference in expansion, they expand and contract by the same amount, and there is virtually no relative movement between them.

On the other hand, the bottom plate 9 and the lower plate 8, which are integrally fastened to the electrode assembly 10 with bolts, have a large difference in coefficient of thermal expansion and the amount of expansion and contraction between them is different, so that relative movement occurs between them. In this case, since both the bottom plate 9 and the bottom plate 8 are bolted together so that they can slide on the contact surfaces, the electrode assembly 10 and the bottom plate 9 can be moved downward without interfering with relative movement between them. It will move integrally with respect to the plate 8. The tightening force of the bolt in the case of slidingly fastening the bolt is determined by an experiment conducted under the same conditions as above for the materials, surface roughness, etc. of each component.

Note that the fixing of the lower plate 8 and the lid 6 and the fixing of the lid 6 and the container body 5 are the same as in the prior art,
In addition, the material of the electrode holding plates 1, 1 is ceramics,
The container body 5, lid 6, and lower plate 8 are made of aluminum having the same coefficient of thermal expansion, and these materials are the same as those in the prior art.

Next, the operation of the present invention will be explained. When the ambient temperature of the detector changes, the electrode holding plates 1, 1 such as the electrode block 4a and the bottom plate 9 have an extremely small difference in thermal expansion coefficient, so they expand and contract together by almost the same amount, and there is a substantial gap between them. No relative movement occurs.
In this case, among the contact surfaces of both electrode holding plates 1 and 1
Since the surfaces of the two are made of ceramics, they are rough and increase the coefficient of friction, which also makes relative movement between the two more difficult.

On the other hand, the bottom plate 9 and the lid 6 (more specifically, the lower plate 8 which is fixed integrally with the lid 6 as described in the prior art) have a large difference in coefficient of thermal expansion, and the amount of expansion and contraction between them is large. Since they are different, a relative movement occurs between the two. In this case, although the bottom plate 9 and the lower plate 8 are fixed with bolts, they are fastened with bolts so that they can slide on their contact surfaces.
It does not impede relative movement between the two. Therefore,
The lower plate 8 with a large coefficient of thermal expansion is the electrode holding plate 1, 1.
This results in sliding movement with respect to the bottom plate 9.
The contact surfaces between the bottom plate 9 and the lower plate 8 can be machined to be smooth due to their materials, which facilitates relative movement between the two. It goes without saying that the relative movement between the two is within the range of play between the bolts that fix the bottom plate 9 and the lower plate 8 and their holes.

Because the bottom plate 9 and the lower plate 8 slide on the contact surface, the relative position and relative dimensions of the electrode block 4a etc. do not change, so the container containing the electrode block 4a etc. and the lower plate 8, which has conventionally occurred, can be removed. 7
Electrode blocks 4a, 4 due to the difference in thermal expansion coefficient between
It becomes possible to suppress changes in pitch Pb between adjacent electrode plates such as between electrode plates B. Therefore, the pitch Pb is set to the pitch of the intermediate part of the electrode block 4a etc.
It becomes possible to maintain the same pitch as the Pi.

[Effects of the invention] As explained above, the invention provides a single unit made of a material with a coefficient of thermal expansion that is the same as or similar to that of the electrode holding plate between the lid that constitutes the container and the electrode assembly inside the container. A bottom plate is interposed, and each electrode block and the bottom plate slide integrally between the bottom plate and the bottom plate due to the difference in thermal expansion that occurs between the bottom plate and the electrode assembly and the container and the bottom plate. Since each electrode block and the bottom plate are fastened to the bottom plate with bolts through the bottom plate, even if the ambient temperature of the detector changes, the electrodes adjacent to each electrode block can It is possible to prevent pitch changes between the plates, and the pitch can be maintained at the same pitch as the middle part of each electrode block.

[Brief explanation of drawings]

The figure is a partially sectional perspective view showing an embodiment of the ionization chamber type radiation detector of the present invention. 1... Electrode holding plate, 2... Signal electrode plate, 3...
High voltage electrode plate, 4a, 4b...electrode block, 5
... Main body, 6 ... Lid, 7 ... Container, 8 ... Lower plate,
9... Bottom plate, 10... Electrode assembly.

Claims (1)

[Scope of utility model registration request] It has a pair of flat electrode holding plates with a large number of grooves cut radially toward the radiation source on one side and the grooves are placed facing each other. It consists of an electrode block formed by alternately adhering and fixing electrode plates and high-voltage electrode plates, a box-shaped cylindrical body with one side open, and its lid, and has a larger coefficient of thermal expansion than the electrode holding plate. A flat plate-shaped container made of the same material as the lid and integrally fixed to the lid, and an electrode assembly consisting of a plurality of the electrode blocks is placed inside the container over the entire length of the inner surface of the lid. In an ionization chamber-type radiation detector in which a lower plate is fixed with bolts to accommodate the lower plate and an ionized gas is sealed, there is a space between the lower plate and the electrode assembly that is the same as or similar to the electrode holding plate. A single bottom plate made of a material with a high coefficient of thermal expansion is interposed, and the difference in thermal expansion generated between the bottom plate and electrode assembly and the container and bottom plate causes each electrode block to be separated between the bottom plate and the bottom plate. An ionization box type radiation detector characterized in that each of the electrode blocks and the bottom plate are fastened to the lower plate with bolts via the bottom plate so that the electrode blocks and the bottom plate can slide integrally.